The Fenrir Virus
by RageDragon24
Summary: When an animal attacks and kills at SGH, Callie investigates and finds herself thrown into the supernatural world that exists with our own. Obviously AU, and inspired by the coming of Halloween.
1. Chapter 1

Rated M for strong violence and gore.

Disclaimer: I don't own Grey's Anatomy or its characters.

"Dr. Torres? Were you aware of Addison's return?"

Callie looked up from her paperwork and noticed Dr. Derek Shepherd leaning in the doorway of the staff lounge, his arms crossed. Addison came back from Los Angeles already? She was only gone for two months. Callie smiled.

"No, Dr. Shepherd, I had no clue she was coming back."

Derek grinned. "I thought you two are best friends."

"'Were' is more like it. She never told me she was leaving Seattle and never returned my calls, so I have no clue what we are now." She closed her binder and stood. "Where is she?"

"Last time I checked she was with the Chief. Good luck." And with that Derek left.

Callie Torres travelled across the hospital to the Chief's office just in time to catch up with Dr. Addison Montgomery as she shut the door behind her. She was wearing a small black dress with matching black stilettos and her hear was pulled back into a French braid. Callie reached out to tap Addie's shoulder but before she even touched her, Callie's hand was crushed by Addison's right fist. Callie was amazed at the fact that even though Addie was facing the other direction she was able to locate Callie's hand behind her head. Must've been a freak coincidence. Addie turned and when she realized that the hand belonged to Callie, she dropped it.

Callie rubbed her right hand with her left and winced in pain. Her hand had already begun to swell. "Jeez Addie! Were you working out or something?" She clenched her right hand repeatedly to try to will the pain away. "I think you broke my hand!"

Addie lifted her hand to her face and stared at it absentmindedly before responding. "Oh! Um, yeah, I was doing Pilates in LA." She lowered her hand and cocked her head to the side. "I hear you are the Chief Res here?"

"Yeah, I am. It's a lot hard-"

"Could you lend me one of your residents for my hysterectomy tonight?" Addison's face started to twitch nervously.

Callie looked at her binder for an available resident. "Let's see…Dr. Stevens is open for the rest of the night. You can take her."

Addison spun around and started to leave. "Have her meet me in the on call room at 8 PM," she called over her shoulder before she disappeared into an elevator.

"Um…ok…" Callie softly said to herself as she left for the staff room. She beeped Izzie and told her where she was assigned as she walked. _Why was Addison acting so weird? Why didn't she want to talk to me?_ Many questions filled Callie's mind as she entered the lounge and laid down on the couch. She felt that a nap was in order and she shut her eyes.

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The shrill tone of the hospital alarm caused Callie to spring of off the couch, spilling her binder onto the floor. She looked out the window and noticed hospital workers sprinting down the halls, panicked, their faces white in horror. Callie opened the door and hollered out to Alex Karev as he herded his interns in front of him.

"Karev, what the Hell is going on?!"

"There was an animal loose on the fourth floor. We got a MASCAL situation!"

Callie joined the fray of people and continued to converse with Alex. "Why are we evacuating? Shouldn't we go and rescue the survivors?"

"The animal is still up there! It killed Izzie!" Alex ran ahead of Callie and continued to help people keep up. Callie stopped dead in her tracks as the flow of people split around her like a river around a rock. A resident died on her watch. Without thinking, she sprinted against the terrified nurses and doctors and ran up the emergency stairs to the fourth floor.

The glass window of the door was smeared with a bloody handprint and spattered with specks of fresh blood. Callie carefully opened the door and a partially headless corpse fell to her feet. She leaped back against the wall of the stairwell and screamed. She quickly covered her mouth when she remembered that the animal was reportedly still hiding on this floor. She slowly walked over the body into the surgical wing and started to gag when the stench of copious amounts of gore and blood hit her senses. Along the wall to her right she spotted three nurses, their bloodied bodies slumped to the ground, their intestines spilt and their limbs torn from their joints. The windows to Callie's left were almost all broken, save for two that must've been spared.

She continued down the hallway, careful not to step in the puddles of blood or trip over a random limb. As she neared the on call room, she noticed a pair of light blue scrub adorned legs sprawled into the hallway, the rest of the body hidden from view. Callie knew this had to be Izzie and when she arrived at the room, her heart dropped at the sight of Izzie's body lying on the on call room's floor. Her throat had been ripped out but she still seemed to be in better shape than the four corpses Callie had seen. Izzie's death had been quick; she bled out in a matter of seconds. Callie reached down to pick up Izzie's body, but she heard someone's raspy voice in the doorway behind her.

"Don't pick her up! This is a crime scene…or something." The voice belonged to Mark. Callie turned to him and was shocked at how injured he was. His arms were covered in deep lacerations; he had wrapped his arms in yards of gauze to slow the bleeding. Blood flowed freely from his nose as he spoke. "I think that beast is gone. That bitch bit me!"

"Shhh, let's just get out of here." Callie stood upright and began to lead Mark into the hallway when he spoke again.

"No! Addison's up here somewhere. I can't leave her."

Callie dreaded the thought of her friend ripped to shreds and shuddered to think that the corpse at the stairwell doorway could be Addison. She glanced down the hall at the headless body and sighed a sigh of relief that it was a man. "She probably made it out ok. She's probably downstairs in the parking lot waiting for you. Come on, let's go."

Mark reluctantly followed. As they neared the headless man they heard a small cry for help behind them. "Pleasssse hhhelp." The two turned and faced a bloodied and naked Addison who was dragging herself across the floor, her legs leaving a trail of crimson behind her. Her body was covered in cuts and bruises and blood poured from her mouth.

"Oh my God! Addie!" Callie screamed as she ran to her side. She removed her lab coat and draped it over Addison's shoulders. "Can you get up?"

Addison wheezed and nodded her head. Callie pulled her to her feet and both she and Mark led her out of the bloodbath of the fourth floor. When they exited the hospital they were swarmed by the press, the flashbulbs blinding the trio. Callie could hear reporters yelling questions, but she couldn't comprehend anything but the sound of her breathing within her own body. Soon the paramedics broke through the crowd of reporters and took both Mark and Addison away to one of thirty or so ambulances in the lot. Callie continued on through the crowd, the mass of people a surreal cloud of flesh and lightning. She strode on, to where she had no clue, but she didn't want to be here.

A male police officer appeared in front of her and took her by her hand. Callie floated along with the man, not knowing nor caring where he led her. She found herself in the back of a squad car and within seconds, she was moving away from the Seattle Grace lot. People were watching her leave, faces still blank. As the car sped away, she could see the SWAT team charge toward the hospital, guns drawn and helicopters hover overhead, directing their lights on the walls of SGH. That was the last thing she remembered before she blacked out and fell to the cool leather seat of the squad car.


	2. Chapter 2

Disclaimer: I do not own Grey's Anatomy or any of its characters.

Rated M for violence, gore, and language.

Callie's eyes fluttered open. She was still inside the back of the squad car. She was still too weak to sit up so she continued to lie on the leather seat and stare upwards at the buildings of downtown Seattle. She must not have slept for long she realized as she quietly listened to the police officer's radio. _So, it wasn't a dream. People are dead and you were there._That realization struck a nerve with Callie and a lone tear fell down her cheek. _Did George make it? Of course he did he was off tonight. Did he know what happened? Is he worried; afraid?_ Callie's chest sank as she began to weep.

The sudden slamming of the brakes threw Callie to the floor with a soft thud. _Now what?_ She wondered as she sat up. Someone had run out in front of the car and the officer had braked hard to avoid hitting the pedestrian. The shadowy figure moved to the side only slightly to get a better view of the officer.

The man rolled down his window and started to yell at the figure. "What the Hell is wrong with you; walking out in the street like that?!"

A woman's voice. "Release the woman."

"I'm taking her in for questioning. And who do you think you are telling me to release her?"

And with that the shadowed figure sprang to the driver's side window and grabbed the officer by his throat. He was yanked out easily by the unknown assailant and was flung into the trunk of a nearby oak tree in someone's yard. He laid curled in a ball at its roots, out cold. The car started to lurch forward as it wasn't parked but it hit the curb to the left and stopped. Callie started to try to escape by kicking out the windows but failed miserably. The figure opened the driver's door and sat down. Callie then recognized the person.

"Yang?! What the fu-"

"Shh! Shut up Torres." Cristina turned and faced Callie. "I bet you have tons of questions, but you are gonna have to shut up until I tell you otherwise." Cristina reached her fingers through the metal mesh that separated the felons from the officers and ripped it apart like it was made of paper. "Climb through. I'll catch you outside."

When Callie finally escaped the squad car she opened her mouth to speak only to have Christina's hand pressed against it. "What part of 'shut up' do you not understand? You are not safe. Now follow me."

Cristina led Callie into the nearby bushes of someone's property and when they finally exited them, they were in a small park. They continued on until Cristina tossed her left hand up, warning Callie to stop. Cristina looked around and then walked to a large rose bush. She dragged her motorcycle out from behind the bush and waved Callie to her. They soon sped off in the darkness, the roar of the engine echoing against the buildings.

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After an hour or so of weaving throughout the city down what seemed to be every alleyway in Seattle, they stopped in front of an abandoned warehouse.

"Ok, get off," commanded Cristina and Callie did as she was told. She leaped off the back and assisted Cristina in hiding the motorcycle behind a dumpster. Cristina shot a couple of glances in every direction and then whispered, "Follow me."

Cristina opened the rusted door and led Callie inside. Callie couldn't help but to cough as she entered the derelict building. Faint beams of moonlight filtered through the broken windows near the ceiling and fell to the floor, leaving their trails of light visible in the dusty air. Old wooden crates sat everywhere, some stacked as high as the rafters. They continued onwards through the maze of crates. They soon neared an office door and Cristina flung the door open.

"Once we get in here, you can talk. I'm quite sure you have many questions and I will answer them as well as I can." Callie entered the dark office. She noticed papers spread across the floor blackened by years of shoeprints entering and exiting the office. Many of the trails let to a large metal cabinet and disappeared. The click of the doorknob as the door closed caused Callie to jump. The lights were turned on after the door was shut, casting an eerie glow. Cristina took off her leather jacket and tossed it aside. "So, what questions do you have for me?"

Callie glared at Cristina. _How could Yang be so calm?__ And where can I begin with the questions? _

Callie pulled an empty filing cabinet over to the desk that Cristina sat on and took a seat upon it. She still couldn't comprehend what all had gone on in the last few hours. She could see that Cristina was becoming impatient so she threw out a random question. "Um…so what is going on?!"

"That's all you could come up with? You haven't had the chance to speak in a few hours and that's all you can ask?" Cristina crossed her arms across her chest.

"I don't fucking know where to begin! I had a resident killed by some fucking animal, two attending are injured, SGH is in lockdown, and the ORs are destroyed! At this moment, I really can't figure out what to ask you!" Callie couldn't help but to angrily yell at Cristina. "I'm sure you have all the answers, so why not tell ME what's going on?!" She had jumped to her feet, sending the metal cabinet crashing to the floor.

Cristina did not flinch. She continued to stare into Callie's eyes like a tiger eyeing its prey. When she began to speak, her voice was ice cold. "That attack that occurred was not done by an animal. Only one creature in existence could do that. It was a Lycan."

Callie raised an eyebrow. "A 'lycan'? A wolf? So you're telling me that a wolf somehow flew through a window on the fourth floor and-"

"Not a wolf, Torres. A Werewolf."

Callie scoffed and started towards the door. "Ok, you are officially crazy. I'm not going to stand by as you spew shit from your mouth." She reached for the door but found herself thrown back down to the floor. Cristina sprung up into the air like a cat and landed on top of Callie, her hands pinning down her shoulders.

"You are not leaving. If you leave, you will die!" hissed Cristina. "I will personally rip your head off if you try to escape again without my release! "

Cristina stood up, leapt back onto the desk, and perched there like a vulture. Callie sat up and rubbed her head. "Ok, I'm not getting answers; I'm just getting more confused."

Cristina smiled and slid off of the desk. "I figured you wouldn't understand, so let's go on a little field trip." She opened the large, two door cabinet against the back wall with the footprints leading to and from it. It was completely empty; Callie noticed that the cabinet didn't even contain shelves. Cristina lifted out a plywood plank from the bottom of the cabinet and revealed a large hole in the floor. Without saying a word Cristina jumped into the darkness. "Come on, Torres. Jump or I'll make you jump!"

Callie sat on the rim of the hole and slipped into the darkness once more. Within a second, she splashed down into cold shallow water that came up to her waist. She started to panic. She couldn't see anything outside of the single beam of light from the office above. A rat swam by and disappeared once more. _I'm going to die down here. It's over…_

Something grabbed her left shoulder and dragged her to the left out of the light. Shrieking, Callie fought back, fists flying.

"Stop it! It's me!" It was Yang's voice. Callie dropped her fists.

"You could've told me that before you grabbed me, you know?!"

"Yeah, but that wouldn't be fun."

They soon reached the water's edge and Callie, blinded by the lack of light, felt around for an edge to pull herself out on. When she was out of the water, Cristina's hand found hers and Callie was led away in the darkness.

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After what seemed to be forever, Callie could see in the distance a faint light.

"Thank God, some light!" Callie was relieved to get out of the dark.

"Meh, I do better without."

"Yeah, I was wondering how you could navigate this place." A thought sparked in her mind. "Are you the werewolf? 'Cause if you are, I don't taste very good." It sounded like a joke, but Callie was being serious.

"Please!" Cristina spat with disgust in her voice. "I am not a flea-bitten bitch!"

"I noticed you have some crazy made moves back there. Have you been working out too?"

"No."

There were a couple of minutes of silence, before Callie spoke again. "I'm going to take a wild shot at this, but after tonight the world's gone a little crazy. You must be a 'vampire', sent to capture me and to squeeze answers out about the 'werewolf' attack." She laughed as much as one could in the same situation as her.

Cristina let go of Callie's hand and began to clap. "Bravo Torres! You've got it all figured out and I didn't have to explain."

They walked up to door that was illuminated by the dull light Callie had seen five minutes prior. Upon entering the room Cristina flicked on the light by the door. The bright light of the single light bulb that hung from the ceiling revealed the contents of the rather large room. Random skulls and bones were laid out on shelves that adorned much of the walls. There were old relics in a glass curio cabinet and rolled up parchment in the corner. And against the fall wall sat a desk with a dusty computer and a large flat screen panel that showed the map of the United States. Green blips speckled the entire US, some moving faster than others. Most stood completely still. Callie picked up a large skull from the shelf to her right.

"That's a skull from an Alpha Lycan. It's a male, you can tell by the size of the canines," informed Cristina as Callie observed the skull. It was very much human, except for the maxillary area, which was stretched out and formed a rudimentary snout. The roots of the teeth were so long and deep, they broke through the bone. The canine teeth were at least three inches long and that wasn't including the roots. Callie set the skull down and picked up the mandible that was beside it. The jaw had also been stretched forward to match the snout's length. After setting down the mandible she observed the other various bones that were nearby. Every bone had been thickened and some stretched, but they were still humanoid in structure. Callie couldn't believe it: the legend of the werewolf was true.

"I'm amazed. I really don't know what to say." After seeing the bones, she couldn't debunk the myth anymore. She sat down on the chair in the corner and stared at some of the weapons that hung from the walls between the shelves.

"Then I will begin." Cristina sat down on the computer chair and began her story. "Vampires have been around since humans first evolved. A genetic mutation caused a number of humans to require more iron in their diets than usual. Most died, but a few learned to hunt better and more efficiently…sometimes with their teeth. But even better hunting couldn't sate the need for iron so we began to cannibalize our own species. We were hunted to near extinction and we hid.

"This is where lycans come into the picture. During our years of exile a sickness was uncovered as we began to move northward into Europe and Asia. It caused madness and disfigurement to whoever feeds from wolf carcasses. Something didn't work right when lupine blood protein mixed with vampire blood. Hair grew uncontrollably, the bones twisted and stretched, eye teeth lengthened. The first lycans were created and have been a plague to us vampires ever since.

"Unlike vampires, who pass their genes on generation to generation, lycans infect others and the victims soon transform into werewolves as well. Neither human nor vampire is safe from the disease. Once infected, they are doomed to be a ravenous beast for the rest of their lives."

Callie didn't want to interrupt, but a question burned in her mind. "What does this have to do with me?"

"I'm glad you asked! I need you to tell me everything that has happened tonight, and we'll go from there."

Callie told everything knew to Cristina, who patiently listened to her. She spoke of the mass evacuation of the hospital, the massacre on the fourth floor, and about Mark and Addison surviving the attack. _Oh no! They are infected__ too__…_Cristina frowned at hearing the news of the newest lycans.

"And then you came along and busted me out of the car and-"

"That's enough Torres. It seems we have a major problem on our hands here. We are no longer dealing with one lycan here. We are dealing with three or more. This is going to be a challenge." She spun around and started typing frantically at the keyboard. The panel on the wall started displaying information on different vampires in the Seattle area. "Every vampire by Vampire Law must be IDed at soon as possible after birth. Those green specks are vampires. I am one of only seven in Seattle."

"Why are you required to get micro chipped?" Callie inquired as she moved to Cristina's side.

"For this reason you see before you. When we come of age, we are needed to work together to end a Fernier Virus outbreak." Cristina saw Callie look at her quizzically and she continued to explain. "The Fenrir Virus is what creates lycans. It is named after the mythical wolf of Norse lore that grew so large that when he opened his mouth, his nose would touch the sky and his jaw dragged along the ground. The virus is known to spread through saliva and blood so far. If we didn't destroy every lycan we came across the virus would have probably mutated by now."

"To what?"

"An airborne disease. If this happens, every human on Earth is in danger." Cristina stared at the screen and tapped madly at the keys. "I have sent a message to all vamps in the city and the surrounding area to come to this room if they are able to fight. Hopefully by this time tomorrow we will have enough on our side to take out the three lycans."

"I get that vampires can be infected, by why do you care if the humans are wiped out? If we are all gone, you don't have to live in the shadows anymore."

"You are such a naïve one, aren't you Torres" Cristina sneered and she strode to a crossbow that hung on the wall. She took it down and inspected it. "Humans are our sustenance. Human blood sates our hunger better than any type of blood or iron supplement we use to keep us alive."

Callie frowned and grew pale at the thought of humans as livestock. Yet Cristina continued on.

"We don't kill humans outright like in the days of old. It's outlawed. However, who do you think runs the blood banks? We do. That's why there is constantly a shortage of blood. Humans have stopped donating as much as they used to but our need of blood never ceases. Many medical facilities are run by vamps as well but you'd never have known."

Callie's head spun and her stomach lurched at the reality of it all. She was nothing more than food for something else. _So much for human__s being on top of the food chain_. She couldn't trust anyone anymore. Was George a vampire? Bailey? The fucking Chief? Her heart pounded in fear. "So…why are you a surgeon? You are nothing more than a glorified vet!"

"This is true. If I practice great livestock husbandry, my patients may live on a reproduce, not knowing that they are prey. But I cannot stand actual veterinarians though. The idea of pets having pets is weird to me." Cristina handed Callie a silver dagger, its hilt intricately designed with wolf skulls and serpents. "You need to take that with you for protection. Most myths about vamps and lycans are false and utterly stupid if you ask me, except for the silver allergy lycans have."

"Couldn't you have given me a gun or something? I would think that it would be a moot point to stab a lycan if it was already on me." Callie stabbed at the air fiercely, pretending that she was some sort of ninja warrior. "Yeah, if this is what I get, I'm totally screwed." She set the dagger down and crossed her arms.

"Silver bullets are expensive and can only be used once. The bolts I use for my crossbow are reusable, as is your dagger. And your dagger is deadlier than you give it credit for." Cristina tossed Callie the leather sheath for the dagger. "I suggest you take your weapon. You haven't seen the last of the lycans. Come."

Cristina led Callie out of the room and back out into the pitch black tunnel. After fifteen minutes of walking blindly, Callie was led up an access ladder on the wall. Cristina tossed the manhole cover aside and helped Callie out onto the pavement. They were in the same alleyway that Cristina's motorcycle was hiding in. "Well! Isn't that convenient!" exclaimed Callie with a smile.

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It was 3:30 in the morning when Callie finally reached the Archfield Hotel. She stepped off of the bike and fixed her jacket and hair. What would George say if he saw her like she was just five minutes before? She nodded to Cristina and began to walk to the doors.

"Torres!" Cristina called.

Callie reluctantly came back. "Yes?"

"You didn't hear anything from me. I have broken many laws tonight for your sake. Don't screw me over or you will be sorry you ever met me."

"I'm already sorry I met you, Yang."

Cristina grinned. "Good. Then I trust you'll keep your mouth shut. I'll be seeing you soon. I'm sure of it." With a roar of her chopper, Cristina was gone, leaving Callie alone in front of the Hotel.

Trying to play it cool, Callie walked into the lobby as cool as possible. She didn't make eye contact with anyone as she entered the first elevator that opened up. When she arrived at her floor, she ran into George, who was standing in front of the elevator. "George?! What is going on?"

George threw his arms around her and held her tight. "Callie! I was so worried! I heard what happened at the hospital tonight!" He dropped his arms and began to inspect her body. "Are you ok? Did you get hurt?"

Callie rolled her eyes at her husband. "No, George. I'm okay. I'm just really tired. Can we just go to bed?"

"Yes, of course. I'm sure you had a rough night, Cal." George said as they walked hand in hand to their room.

_You have no idea_ thought Callie as she opened the door and entered the room. She hoped that she had seen and heard the last of lycans and vampires, but figured that she'd never be that lucky. When her head hit the pillow minutes later, she was old cold.

_A/N: I know this chapter was a little boring, but your patience will be rewarded with the next chapter, I promise! _


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